Plants perennial
herbs, with rhizomes, glabrous. Young stems or twigs rounded or slightly
angled, not winged. Leaves sessile or short-petiolate, the blades sometimes
clasping at the base. Flowers often relatively few, actinomorphic. Calyces of 5
sepals. Corollas of 5 petals, these pink, less commonly flesh-colored, not
persistent at fruiting. Stamens 9, in 3 groups of 3, the filaments within a
group noticeably fused toward the base. Staminodes 3, alternating with the
groups of stamens, appearing as ellipsoid, yellow to orange glandular bodies
attached at the base of the ovary. Pistils of 3 fused carpels. Ovary 3-locular,
with axile placentation. Styles 3, free to the base, loosely ascending at
flowering, the stigmas capitate. Fruits capsules, narrowly oblong-ovoid,
2–3 times as long as the sepals. Seeds numerous, 0.8–1.2 mm
long, ovoid-cylindrical, not flattened, rounded to bluntly pointed at the ends,
the surface with a network of fine ridges and pits, dark brown. Eight to 10
species, eastern U.S. and Canada, Asia.

Steyermark
(1963) and various other earlier botanists treated Triadenum as a
section within Hypericum, but Gleason (1947) argued persuasively that
the odd staminal characteristics of the species and the petal color warranted
the group’s recognition as a separate genus. Subsequent workers (see Wood and
Adams, 1976) noted differences in vascular patterns of the flowers and corolla
positions in the buds. Thus, most recent authors of floristic manuals (Voss,
1985; Kaul, 1986; Gleason and Cronquist, 1991) have maintained Triadenum
as a separate genus.